12-O-Tetradecanoyl-phorbol-13-acetate (TPA), the most powerful agent in the phorbol series, initiates a series of metabolic events in granulocytes which are also activated during phagocytosis. We have found that human promyeloid cells derived from a patient with acute promyelocytic leukemia do not respond, or respond poorly to TPA. During in vitro maturation, the cells achieve the ability to respond to TPA as measured by an increase in hexose-monophosphate shunt activity and protease production. On this basis, we propose to study the development of TPA-responsive systems during the maturation of human myeloid cells in vitro to determine: 1. Whether the enzymatic activities involved in the response of granulocytes to TPA can be detected prior to development of TPA sensitivity; 2. Whether other tumor promotors can induce the same responses; 3. Whether all of the enzymatic activities involved in the TPA response appear simultaneously or sequentially; 4. Whether anti-inflammatory glucocorticoids which interfere with the tumor-promoting activity of TPA have any selective effect on the occurrence or activity of the enzymes involved in the response. We have also found that TPA-treated granulocytes are capable of inhibiting mitogen-induced lymphocyte activation. We intend to determine whether this inhibitory activity is unique to TPA-treated granulocytes or whether it can be evoked by any agent which activates granulocytes to phagocytize. We also intend to determine whether inhibition is mediated by cell-to-cell contact or by release of an inhibitory compound from treated granulocytes. Finally, we will evaluate each of the TPA-induced reactions in granulocytes in terms of their suitability for use as bioassays utilizing normal human cells for detecting agents with potential for acting as promotors.